1. Field of the Invention
The present invention relates to a data recording method which is suitable for use when data is recorded to, for instance, an optical disc.
2. Description of the Prior Art
The development of the WORM (Write Once, Read Many) type optical disc and the erasable and rewritable optical disc (for instance, magneto optical disc) has progressed. In such an optical disc, one track is divided into a plurality of sectors and data is recorded/reproduced on a sector unit basis. For instance, in the recording format for optical discs having a diameter of 5.25 inches, one track is divided into 17 sectors and data is recorded there.
In the conventional optical disc, in order to cope with a burst error or the like, the encoding of an error correction code is executed for every sector and a parity for error correction is generated and added.
For instance, among the recording formats of the optical discs having a diameter of 5.25 inches, there is a format which uses an LDC (long distance code) as an error correcting method. In the recording format using the LDC, for instance, control data and a CRC code for error detection are added to the user's data of 512 bytes, data is written into a buffer memory in the horizontal direction, error correction encoding is executed in which respective columns are used as an encoding series, and a parity of 16 bytes per series (5.times.16=80 bytes per sector) is added. The data is read out in the horizontal direction and recorded into each sector on the optical disc.
As mentioned above, in the case of generating and adding a parity for error correction of 16 bytes to one series, the error correction can be executed for up to eight bytes per series. Data is arranged into five columns, the error correction code is added by using each column as an encoding series, and the reading/writing operations are executed in the horizontal direction, so that an interleave of five bytes is executed. Therefore, in this case, it is possible to cope with the generation of burst errors of up to 5.times.8=40 bytes. The defects of 40 bytes correspond to a length of about 300 .mu.m at the innermost rim of the disc.
As mentioned above, in the case of an optical disc having a diameter of, for instance, 5.25 inches, it is possible to cope with burst errors corresponding to for instance, 40 bytes by the LDC. However, in the recording medium such as an optical disc on which data is recorded at a high density, it can happen that fairly large burst errors are generated. In such a case, the error correction cannot be executed by the LDC as mentioned above.
Therefore, when recording data onto an optical disc, a verification is made to see if errors equal to or exceeding a predetermined value have been generated in the sector into which data is to be recorded or not. The sector in which the errors of the predetermined value or more are generated is regarded as a defective sector. The data to be recorded into the defective sector is recorded into an alternate sector. In this manner, the alternate sector process as mentioned above is performed.
However, even if such an alternate sector process is executed, it is impossible to cope with large burst errors which are generated after data was recorded. If large burst errors are generated in the read only disc, the alternate sector process cannot be executed.